This invention relates generally to xe2x80x9cpolyxe2x80x9d bag making machines and, more particularly, to mechanisms for operating the seal bar component of such bag making machines.
Poly bag making machines are well known. Draw rolls pull a web of plastic film material from a supply. A transverse cutting and sealing bar (hereinafter referred to as a seal bar), is situated after the draw rolls and mounted for reciprocation to cut and seal the web after each web index movement to form individual bags. The bags are carried to a stacking station on a stacker conveyer by means of a rotating vacuum arm assembly. Bag machines of the type described are well known. For example, a typical bag making machine of this type is The Polystar 9000 available from Ro-An Industries Corp. of Maspeth, N.Y., U.S.A.
Generally, bag making machines of the type described are powered by a main drive motor that drives a main drive shaft which in turn drives the various components of the bag making machine, including the draw rolls, seal bar, vacuum arm assembly and stacker conveyer, through conventional mechanical linkages including, gears, pulleys, crank and rocker arms, clutch/brake systems, cams and cam followers and the like.
Recently, servo drives have been used to drive various components of bag making machines. For example, servo motors are used to drive the draw rolls and stacker conveyer components of bag making machines in a coordinated manner through a servo-controller in order to reduce the number of cycle interrupts required within which to index the stacker conveyer when a stacker station has been filled with bags. In this connection, reference is made to U.S. Pat. No. 5,338,281 to Terranova, the disclosure of which is incorporated herein in its entirety.
It has also been proposed to replace the conventional cam and cam follower mechanism for reciprocating the seal bar by a servo motor or servo valve to drive a linkage to raise and lower the seal bar of the bag making machine so that the position, and motion of the seal bar, including its dwell time in the fully down and sealing position, can be controlled independently of the machine speed and other components of the bag machine. In this connection, reference is made to U.S. Pat. No. 5,230,688, to Hatchell, et al., the disclosure of which is incorporated herein in its entirety.
However, reciprocatingly driving a seal bar by a servo motor or servo valve requires substantial modification of relevant components of the bag making machine. Moreover, any benefits obtained by the substantial modifications required to provide an independent operation of the seal bar are often outweighed by the substantial expense of the modifications which are required to accomplish this end.
Moreover, prior arrangements for reciprocating the seal bar in bag making machines are designed to raise and lower the seal bar in a uniform manner, i.e. so that the seal bar is lowered onto and contacts the plastic web uniformly over the entire width at the same time with a constant degree of penetration. While such operation is generally suitable, there are some applications,, e.g. in the sealing of certain multiple ply plastic webs, where it would be desirable to first lower one end of the seal bar onto the web and then gradually lower the other end so that the seal bar engages the web progressively from one edge of the web to the other. Other applications make it desirable to have different degrees of penetration of the web by the seal bar at respective end regions of the seal bar. However, it is not possible to accomplish these functions using conventional mechanical and servo controlled mechanisms for raising and lowering the seal bar.
Accordingly, it is an object of the present invention to provide new and improved mechanisms for driving a seal bar in a bag machine.
Another object of the present invention is to provide new and improved mechanisms for adjusting the position and movement of a seal bar in a bag making machine which is controlled by the machine""s drive shaft.
Still another object of the present invention is to provide new and improved mechanisms for adjusting the position and movement of a seal bar in a bag making machine which is controlled by the machine""s drive shaft and which enables a selective adjustment of the dwell time of the seal bar.
Yet still another object of the present invention is to provide new and improved mechanisms for adjusting the position and movement of a seal bar in a bag making machine in which the raising and lowering of each respective end of the seal bar is independently adjustable.
Briefly, in accordance with the present invention, these and other objects are attained by providing an improvement in the mechanism for reciprocatingly raising and lowering the sealing bar in which the movement and position of the sealing bar are controlled by the drive shaft and are selectively adjustable by one or two separate servo-drives.
A main link is coupled to a seal bar drive shaft for movement in direct response to its rotation. A second link is movably coupled to the main link. A servo-drive system including a servo motor or servo valve is coupled to the second link for adjusting the position of the second link with respect to the main link while the main link is moving in response to the rotation of the drive shaft.
Separate mechanisms may be provided for controlling and adjusting the position and movement of each one of the two ends of the sealing bar, independently of each other, in a coordinated fashion. Independent adjustment allows for variations of the sealing profile and seal bar penetration.